The present invention relates to an oil drain plug for use with the oil pan of automobile engines.
Conventionally, automobile engines are provided with a mechanism for circulating lubricating oil (oil) through predetermined portions in order to allow the moving parts to move smoothly. The oil will be degraded over time with use to lose the lubricating performance desired. In addition, the oil will be contaminated by particles caused by wearing or sludge. Accordingly, the degraded oil is replaced at regular intervals (in general, at regular distances of travel about 3,000 to 5,000 km) from the viewpoint of preventing damage to the engine body and the like.
FIG. 5 is an explanatory view illustrating an example of an ordinary conventional engine having a configuration for replacing the degraded oil. Oil 100 in an oil pan 102 disposed under the crank chamber is supplied to predetermined portions by means of an oil pump 101. The oil is pressurized and fed by the oil pump 101. Then, the pressure of the oil is regulated by a regulating valve 103. Subsequently, foreign matter such as metal particles, carbon impurities, and sludge, which contaminate the oil are removed to clean the oil via a filter 104. Finally, the oil lubricates each of the portions of the engine and then returns to the oil pan 102 again. Incidentally, the oil pan 102 is generally filled with oil under normal conditions.
As described above, contaminants in the oil are filtered by the filter 104 in general in the course of circulation thereof, however, there is a limit to removing foreign matter by means of the filter. In addition, the degradation of the oil itself with time cannot be avoided. Accordingly, the oil is replaced in the following manner. A plug (drain cock) 106 is first removed from the oil drain hole (drain hole) 105, which is provided in the bottom portion of the oil pan 102 and usually closed tightly, to drain the degraded oil by gravity. Then, the oil drain hole 105 is closed by the plug and new oil is poured from the upper portion of the oil pan 102.
However, the aforementioned oil replacement is rather cumbersome in that the plug is first removed from the oil drain hole 105 and the plug is threaded into the hole again after the oil has been drained. In addition, it cannot be avoided for the operator to be smeared with the oil.
Accordingly, it is also practiced to drain the oil from the upper portion of the engine. For example, this includes a method for vacuuming the degraded oil with an elongated suction tube inserted in the attachment hole for an oil gauge, which is provided for checking the amount of the engine oil and contamination thereof. Also included is a method with the suction tube inserted in the oil filler port (these methods are hereinafter referred to as the “upper drainage methods”).
However, the upper drainage methods can provide no means for checking whether the distal end of the tube has reached the bottom portion of the oil pan since the tube is inserted from above the crankshaft or other complicated mechanisms that are accommodated in a narrow limited space. For this reason or another, it is difficult to completely drain the degraded oil. Thus, it may not be found that the degraded oil has not been replaced properly until the refilled oil is checked. In an extreme case, the refilled oil may be replaced again. In addition, the upper drainage methods have not been employed widely because the methods cannot provide means for readily eliminating metal particles and the like accumulated on the bottom portion of the oil pan.
On the other hand, the method for draining the degraded oil from the bottom of the pan allows complete drainage of oil. By making use of the advantage thereof, improved methods have been suggested to solve the problem of smearing the operator with oil. For example, these methods include an oil replacement method with a permanent fixed plug having a normally closed poppet valve built therein (U.S. Pat. No. 4,745,894 and the corresponding Japanese Patent Publication No. 04-48987). Also included is an oil replacement method with a permanent fixed plug having a normally closed ball valve built therein (Japanese Patent Publication No. 08-170782).
These methods remove the existing oil drain plug 106 of a simple configuration shown in FIG. 5 and substitute for the closing plug 106 a plug (not shown) which has a normally closed valve built therein and is fixed to the oil drain hole 105. At the time of oil replacement, a jig dedicated to opening the built-in valve is attached to the plug to suck the oil 100 in the oil pan 102 under a negative pressure. Then, after the oil has been drained, the jig is removed from the plug and the built-in valve is returned to the closed position to allow new oil to be filled in the oil pan.
This method allows the oil 100 to be forcedly sucked and drained by a suction device, thereby providing a quick draining. Moreover, apart from the first plug replacement, the plug needs not to be removed nor threaded into the oil drain hole again. Furthermore, the method provides an advantage that the operator can drain the oil without being smeared therewith and the surrounding area can be prevented from being covered therewith.
However, when the inventor actually tried draining oil using the plug having the normally closed valve built therein according to the aforementioned prior-art method, it was found that the plug could be incorporated into only limited types of automobiles due to some problems that some automobiles were not adapted to have the plug attached thereto.
Accordingly, a further detailed study was made and it was found that these problems were originated from slight displacements in various mechanisms in the oil pan, which was designed in accordance with specifications different depending on the type of automobiles and which did not always require to be assembled with high accuracy.
That is, the plug having the normally closed valve built therein, disclosed in the aforementioned Japanese Patent Publication No. 08-170782, is adapted to allow oil to flow in from the periphery of the cylinder portion that accommodates the ball valve constituting the normally closed valve. Thus, the ball valve and the portion for accommodating a spring for biasing the ball valve to the normally closed position are attached to the oil pan so as to protrude into the oil pan for a certain length. In this case, presence of a structure on the axial line of the oil drain hole in the oil pan would cause the plug to be insufficiently threaded into the hole, thus resulting in defective attachment. Such a structure includes a baffle plate for preventing the oil from waving during travel, a separator, and a strainer for drawing up oil. In some cases, the plug cannot be attached to the automobile at all due to the design specification thereof. In addition, although the design specification allows the attachment of the plug, a displacement of a few millimeters occurring during the manufacture of the oil pan may make it impossible to attach the plug thereto.
In the case of the plug having the normally closed valve built therein, disclosed in U.S. Pat. No. 4,745,894, the distal end of the plug attached to the oil pan in the normally closed position is placed generally on the same plane as the bottom surface of the oil pan. Thus, this does not raise such a problem that the plug cannot be attached to the oil pan even in the presence of a structure on the axial line of the oil drain hole as described above. However, the plug according to this method is adapted to move the valve body disposed at an edge portion of the plug inside the oil pan into the oil pan to disengage the valve body from the valve seat, thus opening the valve to drain the oil. Thus, the presence of the structure mentioned above would lead to a drawback that the plug can be attached to the oil drain hole but the valve cannot be opened. Accordingly, it cannot be found that the plug cannot be opened until the oil is drained next time. This presents more detrimental effects in practice.
The present invention was developed to improve the plug having a normally closed valve built therein, which requires no removal of the plug and prevents the operator from being smeared with the oil and provides a quick draining, as described above. An object of the present invention is to provide the improved plug having a normally closed valve built therein for draining engine oil, the plug being made available to any automobiles without being affected by a slight displacement caused by the type of automobiles or the assembly of mechanisms in the oil pan.
Another object of the present invention is to provide an oil drain plug which protrudes less downwardly from the bottom of the oil pan to reduce the possibility of damaging the plug due to rubbing between the bottom of the automobile and the ground.
Still another object of the present invention is to provide an oil drain plug of a simple configuration with good mass-productivity to facilitate assembly, thereby providing an inexpensive plug.